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Since March this year I have an MB Pro Red running in parallel with a Davis Envoy system. Before switching to solely using MB readings, I wanted to check for differences between the two systems, both using the same wireless signals from ISS and Soil/Leaf station.
Most delta's, if any, are small and usually due to slight changes in timing, rounding etc, but after 3 months of recording the MB Soil Moisture readings appeared to be up to 40% higher compared to the Davis Envoy system, see chart below.
The plot shows some systematic shifts in data so I plotted the ratio between MB and Davis readings in time.
The delta is becoming smaller with summer nearing. When adding Soil Temperature to the time plot there an inverse relationship visible with MB/Davis ratio. Which reminded me about a note in the Davis manual that soil temperature is used to correct the soil moisture readings: "If no soil temperature sensors are installed, the station will use the default temperature of 75ºF (24ºC) to compensate the soil moisture readings. The soil moisture accuracy will be off by about 1% for each 1ºF (0.5ºC) difference between the actual soil temperature and 75ºF (24ºC)."

In this case the temperature in March was down to 6 degr. C, meaning 18 degr. C = 32.4 degr. F below the Davis reference temperature and thus a 32% reduction applied as correction. That's for the MB /Davis ratio then 1/(100-32)*100 = 1.48 and thus rather close to the 40% difference noted in graphs above between MB and Davis readings of same raw wireless signal.

Is the Meteobridge missing such correction or am I overlooking something?

Meteobridge PRO reads the RF data from the sensor and directly converts that into soil readings (temp and moisture). There is no compensation of the moisture readings by using the temperature readings.

Thanks for the quick reply!
For the moment I will try a correction as Davis suggest. That should then look like: th10hum-corr = th10hum*(100 - 1.8*(24 - th10temp))/100.

But if someone knows a more accurate temperature correction for the Watermark soil sensor, that would be welcomed!

Hi,

I ran into the same problem, just bought Meteobridge Pro for my Davis Vantage Pro station to replace Meteohub on Sheevaplug that recently died.

As Meteohub was the interface to my home automation system, which also manages my garden sprinkler, I am dependent on accurate soil humidity reading.

The difference between the 2 readings needs to be corrected, but I don't know how to do this.

Anybody that can give me a hint how to get this ? I tried the calibrate function, but that cannot change values based on other sensors.

I found the solution myself , rtfm. It is well explained in templates for Meteobridge Pro.
The solution : <SOILMOIST>{*[soil0hum-act:99] * (100 - 1.8*(24-[soil0temp-act:24]))/100 *1}</SOILMOIST>

The only remaining issue is that there is still a little diffence, so the formula is probably not the exact rule used by Davis.

Thanks in advance.

Hello

Where Can i use this Formula to correct the soilmoisture?
I need to correct it in the dataexport template.
Or just correct the soilmoisture in the Meteobridge.